Owing to the inadequate supply risk of petroleum, the prices of petrochemicals keep rising. Moreover, during the production, the use and disposal of petrochemicals, a large number of pollutants are generated and many environmental problems occur. Therefore, the developments of plant-based raw bio-materials are strongly promoted, and they might replace the petrochemical raw materials as the important industrial raw materials in the future. In nature, the lignin resource is only lower than the cellulose. As there are about 50 billion tons worldwide production of the lignin per year, the abundant and low-cost lignin is an important raw material of great opportunities. In addition, the aromatic ring structure of the lignin attributes to good mechanical properties and chemical resistance, suitable as bio-composite materials.
However, the development of bio-composite materials using lignin in the polymer composite materials is still very limited, mainly due to the OH functional group and benzene ring structure of the lignin with strong intermolecular interaction such as hydrogen bonding and π-π attraction, which cause difficulty in the dispersion of the lignin in the polymer matrix. The more the added amount of the lignin, the worse mechanical properties the composite material.
If the lignin is mixed directly with the polyol for foaming, due to the poor dispersion and stability of the lignin in the polyurethane (PU), the more lignin is added the worse compressive strength is obtained. Although ion exchange may be used to modify lignin sulfonate, the treatment of ion exchange significantly increase the production costs.